ON THE ORKNEY ANIMAL. 4^1 



furnish more advantageous levers for the mus- 

 cles. 



In systematic connection, the contiguous verte- 

 bras present to one another the bases of their 

 cones, united by an intervertebral ligament *, The 

 intervertebral space over which it stretches, is 

 .from two to three quarters of an inch. The li- 

 gament itself is very elastic, and about a quarter 

 of an inch in thickness. It is composed of diffe- 

 rent strata, and each stratum of circular fibres. 

 These strata form the inner side of the base, where 

 they firmly adhere ; are reflected on P the inner 

 side of the two cones, towards their apex f ; but al- 

 ways thinner as they advance from the base to the 

 apex, forming every where the lining or internal 

 stratum of the two cones. 



In the wet state, the ligament where it is re- 

 flected on the inner side of the cones, resembles a 

 ligamento-cartilaginous substance in the dried 

 state. This appears under the form of a strong 

 dense membrane. 



The cavity formed by the two cones and the li- 

 gament was filled with a fluid, opaque, whitish* 

 and fetid ; but became less opaque, white and fe- 

 tid, when exposed to the heat of boiling water. 

 One use of this fluid in the vertebrae of fishes, is 

 well known ; it is the ball on which the vertebrae 

 move with the least possible degree of friction, and 

 is infinitely superior to the ball and socket joint 

 in the works of art. There is something similar 



* Plate x. fig. 3.//*/. t %• 4» ?• 



